1. Field of the Invention
This invention relates to a reproducing apparatus and more particularly to a reproducing apparatus having tracking control means for controlling the position of a reproducing head relative to a recording medium.
2. Description of the Related Art
The known apparatuses of the above-stated kind include helical scanning type magnetic recording/reproducing apparatuses. These known helical scanning type magnetic recording/reproducing apparatuses employ five different tracking control methods, which are as follows:
(1) CTL (control) method: A control signal of a given frequency is recorded along the edge of a magnetic recording tape and a tracking control signal is obtained by reproducing this control signal.
(2) Pilot signal superimposing method: A pilot signal of a low frequency is frequency superimposed on a main information signal and a tracking control signal is formed according to the pilot signal when the pilot signal is reproduced.
(3) Area dividing pilot signal method: A pilot signal is recorded in a recording area other than that of a main information signal and a tracking control signal is formed according to the pilot signal when the pilot signal is reproduced.
(4) Index tracking method: A tracking control signal is formed according to a phase difference between a phase detection signal indicative of the phase of a rotary head and a horizontal synchronizing signal included in a reproduced signal. This method has been disclosed in "Television Society Technical Report", Vol. 11, No. 14, pages 13-18, dated Aug. 31, 1987.
(5) Envelope detection method: A head is vibrated and a tracking control signal is formed according to the envelope level of a signal reproduced by the head.
However, the above-stated methods (1) to (5) respectively have the following shortcomings:
(1) In the CTL method:
(i) This method necessitates the use of an additional CTL (control) track and a CTL head. (ii) Since a period through which tracking control information is obtainable is long, the responsivity of tracking control becomes slow. (iii) The position of a fixed head in the longitudinal direction of the tape must be adjusted.
(2) In the pilot signal superimposing method:
(i) The frequency multiplexing arrangement is apt to bring about a code error in the case of digital recording which tends to be affected by a low band. (ii) Since the pilot signal is recorded at a low level to avoid an adverse effect on a main signal, a poor S/N ratio results from this method.
(3) In the area dividing pilot signal method:
(i) It necessitates an additional area, which reduces the area allottable for main signal recording. (ii) The tracking control responsivity is slow as only one or two samples of tracking control information is obtainable per turn of a rotary head. In order to solve this problem, many pilot signal recording areas are necessary for increasing the number of samples. Such arrangement would further reduce the main signal recording area. In the case of a digital audio tape recorder (DAT) in particular, the main signal (or audio data) occupies only 60% of the whole track length with pilot signal recording area provided before and after the main signal recording area. However, in a case where the main signal is video data which requires a high speed and large capacity, at least 90% of the whole track length is allotted for the main signal, thus leaving only narrow areas for pilot signal recording at two end parts of each track. This presents a serious problem for following the curved parts of tracks in furthering the density of recording.
(4) In the index tracking method: detection signal is used as a reference signal. This imposes a limit on the actual sampling rate. Further, the method necessitates a highly precise phase detecting means in order to obtain several samples of the tracking control signal per track. (ii) It is inevitable to have the adverse effect of jitters during one turn of a drum (or cylinder).
(5) In the envelope detection method:
This method is employed in combination with the so-called wobbling or the like in cases where the tracking control is to be performed by moving a rotary head by means of a bimorph element or the like. The method, therefore, requires a moving head and thus results in a very complex, expensive system as a whole.
All the conventional methods thus have various problems in terms of responsivity, accuracy, etc., and have failed to ensure an adequate performance.